1. Field
The present disclosure is directed to global positioning system receivers. More particularly, the present disclosure is directed to a method and apparatus for calibrating a global positioning system oscillator.
2. Introduction
Presently, temperature compensated crystal oscillators (TCXO's) are used to generate a signal with a precise frequency to provide a stable clock signal for global positioning system receivers. Although temperature compensated crystal oscillators are designed for good thermal stability, they still can be subject to frequency drift during initial startup conditions and other conditions that affect the thermal stability. Such conditions can be based on the proximity of the temperature compensated crystal oscillator to other components in the same device, based on the orientation of the temperature compensated crystal oscillator, and based on other variables that affect thermal stability.
Some temperature compensated oscillators may adjust over a long term, but thermal instability can affect global positioning system performance from the short term change. Short term performance can be critical to obtaining initial position fixes as fast as possible, which can be one of the key parameters for navigation systems. One method of overcoming this effect is to utilize large temperature compensated crystal oscillators that have greater thermal mass, which reduces the rate of oscillator change. Unfortunately, the greater thermal mass limits the ability to utilize global positioning systems in small portable device, which require components to be as small as possible.
Thus, there is a need for an improved method and apparatus for calibrating a global positioning system receiver oscillator.